This type of systems for leveling power supply and demand include a system using stationary batteries set in electricity consumers. This system charges the batteries during night when electricity demand is relatively low, and discharges the batteries during daytime when electricity demand is at its peak, thus leveling power supply and demand. Such a power supply and demand leveling system, which uses the stationary batteries, however, requires a large-scale installation. This makes it difficult to employ the system at low cost. To solve this problem, it has lately been suggested to utilize a power supply and demand leveling system, which uses batteries installed in electric vehicles or hybrid electric vehicles (hereinafter, collectively referred to as electric vehicles) instead of using stationary batteries (see Patent Document 1, for example).
The power supply and demand leveling system, which is disclosed in the Patent Document 1, was made in light of the fact that an electric vehicle used for commuting to and from a business institution who is an electricity consumer remains parked during daytime when electricity demand is at its peak, and thus that there is a battery capacity available for use. During peak hours of electricity demand, the system emits electricity that is stored in the batteries of electric vehicles to make up for electricity shortage in business institutions. During off-peak hours, the system charges the batteries with off-peak electricity to prepare for the next peak hours. By so doing, the system levels the supply and demand of electricity and thus decreases the usage of contracted electricity supplied from the business institutions, thereby reducing electricity costs.